The present invention relates to catalysts for the polymerization of olefins, obtained from cyclopentadienyl compounds, organometallic aluminium compounds and water. Homogeneous catalyst systems for the polymerization of olefins are known which comprise a metallocene and the product of the reaction between water and an aluminium alkyl, where the alkyl is other than methyl.
In European Patent Application EP 384 171, catalysts are described which are suitable for the polymerization of olefins and comprise the product of the reaction between:
(A) a metallocene compound of the general formula:
(C5Rxe2x80x2n)mRxe2x80x3p(C5Rxe2x80x2n)MX3xe2x88x92m
where (C5Rxe2x80x2n) is a cyclopentadienyl group in which Rxe2x80x2 is hydrogen, an alkyl, alkenyl, aryl, alkylaryl or arylalkyl radicals having from 1 to 20 C atoms or a group CR2SiR3 or a group SiR3 with R being defined as for Rxe2x80x2, or two (or four) substituents Rxe2x80x2 of one and the same cyclopentadienyl group form one (or two) rings having from 4 to 6 C atoms, Rxe2x80x3 is a divalent radical selected from an optionally substituted alkylene group having from 1 to 8 C atoms, an SiR2, PR or NR group with R being defined as for Rxe2x80x2, which forms a bridge link between two cyclopentadienyl groups, X is hydrogen, halogen, xe2x80x94OMX(C5Rxe2x80x2n)2, xe2x80x94OH or xe2x80x94OR with R being defined as for Rxe2x80x2, or a hydrocarbon radical having the meaning of Rxe2x80x2, M is a transition metal of valency 3 or 4, selected from Ti, Zr or Hf, p is 0 or 1, m is 0, 1 or 2, and, if m=0, p=0 and, if p=0, at least one radical Rxe2x80x2 is other than hydrogen, n=4, if p=1, and n=5, if p=0; and
(B) an alumoxane of the formula: 
in which R1, R2, R3 and R4 can generically be alkyl, alkenyl or alkylaryl radicals having 2-20 carbon atoms.
The alumoxanes (B) can be prepared by reacting the corresponding trialkylaluminium with water in a 2:1 molar ratio. In the embodiment examples, alumoxanes are used in which R1, R21 R3 and R4 are ethyl, isobutyl or 2-methylpentyl groups.
European Patent Application EP 575 875 describes homogeneous catalyst systems for the polymerization of olefins, obtained by contacting the following components:
(A) a cyclopentadienyl compound of the general formula:
(C5R1xxe2x88x92mH5xe2x88x92x)R2m(C5R1yxe2x88x92mH5xe2x88x92y)nMQ3xe2x88x92n
in which M is Ti, Zr or Hf, C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are cyclopentadiene rings substituted in the same way or different ways, the substituents R1 which can be identical or different are alkyl, alkenyl, aryl, alkylaryl or arylalkyl radicals which have from 1 to 20 carbon atoms and can also contain Si or Ge atoms, or are Si(CH3)3 groups, or also two or four substituents R1 of one and the same cyclopentadienyl group can form one or two rings having from 4 to 6 carbon atoms, R2 is a group forming a bridge link between the two cyclopentadiene rings and is selected from CR32, C2R34, SiR32, Si2R34, GeR32, Ge2R34, R32, SiCR32, NR1 or PR1, with the substituents R3 which can be identical or different being R1 or hydrogen, or also two or four substituents R3 can form one or two rings having from 3 to 6 carbon atoms, the substituents Q which can be identical or different are halogen, hydrogen, OH, SH, R1, OR1, SR1, NR12 or PR12, m can be 0 or 1, n can be 0 or 1, being 1 if m=1, x is an integer between (m+1) and 5, and y is an integer between m and 5;
(B) an organometallic aluminium compound of the general formula AlR33xe2x88x92zHz, in which the substituents R3 which can be identical or different are alkyl, alkenyl or alkylaryl radicals which have from 1 to 10 carbon atoms and can also contain Si or Ge atoms, with the proviso that at least one the substituents R3 is other than a linear alkyl group, and z is 0 or 1; and
(C) water.
The molar ratio between the organometallic aluminium compound and the water is between 1:1 and 100:1. In the embodiment examples, the organometallic aluminium compounds used are only triisobutylaluminium and triisohexylaluminium.
In Italian Patent Application No. MI/94A/1516, homogeneous catalyst systems for the polymerization of olefins are described which possess an activity improved over those exemplified in the abovementioned patent application EP 575 875, which systems comprise the product obtained by contacting the following components:
(A) a cyclopentadienyl compound of the formula:
(C5R1xxe2x88x92mH5xe2x88x92x)R2m(C5R1yxe2x88x92mH5xe2x88x92y)nMQ3xe2x88x92n
in which M is Ti, Zr or Hf; C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are cyclopentadiene rings substituted in the same way or different ways, the substituents R1 which can be identical or different are alkyl, alkenyl, aryl, alkylaryl or arylalkyl radicals which have from 1 to 20 carbon atoms and can also contain Si or Ge atoms, or are Si(CH3)3 groups, or also two or four substituents R1 of one and the same cyclopentadienyl group can form one or two rings having from 4 to 6 carbon atoms, R2 is a group forming a bridge link between the two cyclopentadiene rings and is selected from CR32, C2R34, SiR32, Si2R34, GeR32, Ge2R34, R32SiCR32, NR1 or PR1, with the substituents R3 which can be identical or different being R1 or hydrogen, or also two or four substituents R3 can form one or two rings having from 3 to 6 carbon atoms, the substituents Q which can be identical or different are halogen, hydrogen, R1, OR1, SR1, NR12 or PR12, m can be 0 or 1, n can be 0 or 1, being 1, if m=1, x is an integer between (m+1) and 5 and y is an integer between m and 5;
(B) an organometallic aluminium compound of the formula:
Alxe2x80x94(CH2xe2x80x94CR4R5R6)3xe2x88x92zHz
in which R4 is an alkyl, alkenyl or arylalkyl group having from 1 to 10 carbon atoms, R5 is an alkyl, alkenyl or alkylaryl group with a branched chain having from 3 to 10 carbon atoms, or R4 and R5 are fused together to form a ring having from 4 to 6 carbon atoms, R6 is hydrogen or an alkyl, alkenyl or arylalkyl group having from 1 to 10 carbon atoms and z is 0 or 1; and
(C) water.
The molar ratio between the organometallic aluminium compound and the water is between 1:1 and 100:1.
The polymerization yields of the catalysts described in the abovementioned patent applications are, albeit relatively high, not altogether satisfactory if the residence times of the reaction mixture in the reactor are short. This is particularly important in industrial polymerization processes, especially in those which operate continuously, where it is very advantageous to operate with short residence times.
It would therefore be desirable to improve the productivity of the abovementioned catalysts at short residence times.
A It has now been found, unexpectedly, that catalysts for the polymerization of olefins, of the type of those described in the abovementioned patent applications, obtained from particular mixtures of organometallic aluminium compounds, show superior activities at short residence times than the corresponding catalysts obtained from the individual components of the abovementioned mixtures of aluminium compounds.